Streamlined unobstructed one-pass axial-flow pump

ABSTRACT

A blood pump has an impeller rotatably disposed and magnetically suspended within a cavity of a stator by a plurality of magnetic bearings (passive permanent and active electromagnetic) having impeller magnets on the impeller and stator magnets or coils/poles on the stator. A motor includes impeller magnets on the impeller and coils/poles associated with the stator. A single, annular blood flow path extends axially through the cavity between the impeller and the stator, and between the impeller magnets on the impeller and the stator magnets or the coils/poles on the stator.

PRIORITY CLAIM

Benefit is claimed of U.S. provisional patent application Ser. No.60/506,023 filed on Sep. 25, 2003, which is herein incorporated byreference.

This application is related to U.S. patent application Ser. No.______,filed Sep. 24, 2004, which is herein incorporated by reference.

GOVERNMENT RIGHTS

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require that the patent owner tolicense others on reasonable terms as provided for by the terms of GrantNo. NIH HL64378 awarded by the National Institutes of Health (NIH).

BACKGROUND

1. Field of the Invention

The present invention relates generally to axial-flow blood pumpssuitable for permanent implantation in humans as a chronic ventricularassist device.

2. Related Art

An effective and reliable axial-flow blood pump can provide mechanicalcirculatory support (MCS) to thousands of patients each year. Anestimated 4.8 million Americans suffer from congestive heart failure(CHF), a clinical syndrome that involves ventricular dysfunction andultimately a reduction in cardiac output. A reduction in cardiac outputleads to poor perfusion, fluid accumulation, and activation ofsalt-water retention mechanisms. Statistics from the American HeartAssociation indicate that approximately 400,000 new CHF cases arediagnosed each year in the United States, and an estimated 40,000cardiac failure patients die each year due to CHF.

If short-term medical intervention, whether surgical or throughaggressive medications, is not successful, then many of these heartfailure patients become candidates for cardiac transplantation. Due to alimited number of donor hearts available each year (˜2,500), CHFpatients often require MCS as a bridge-to-transplantation and many suchpatients may fail to survive awaiting a donor organ. Ventricular assistdevices (VADs) or mechanical blood pumps have proven successful inbridge-to-cardiac transplant support of patients suffering fromend-stage heart failure and encourage the belief that long-term MCS ordestination therapy is possible. An estimated 35,000 to 70,000 cardiacfailure patients could benefit from long-term MCS each year.

Despite the tremendous need for an effective ventricular assist pump,prior MCS devices have not been entirely successful due to severallimiting factors. Particular concerns and design limitations of currentblood pump designs include: 1) component durability and lifetime; 2)blood clotting or thrombosis due to flow stasis within the pump insecondary flow areas, wash ports, and recirculation regions, andplatelet activation in regions of high shear stress; 3) blood trauma orhemolysis that may occur when blood contacts mechanical bearings orforeign surfaces, and when blood is subjected to higher than normalshear conditions due to rotating components; 4) percutaneous leads whichare needed for the motor and bearing control systems and other supportlines; 5) pump geometry (size, shape, and weight) for ease ofimplantation, patient mobility, avoidance of graft tears; 6) high costof the pump; and 7) high power demand that requires a large powersupply.

Many early blood pump designs were constructed in a pulsatileconfiguration. These required the explantation (removal) of the diseasednative heart and the replacement by the pulsatile mechanical blood pump.These pulsatile pumps, however, have proven to be very complicatedmechanically, are relatively large and have relatively short mechanicallifetimes. An alternative design using a rotary pump leads to the use ofthe mechanical heart as a ventricular assist device which does notrequire explantation of the native heart. The rotary pumps have smallersize and better mechanical reliability. Such a pump aids a patient'sheart by pumping additional blood in parallel with a diseased heart. Therotary blood pump may be connected to the patient's heart in aleft-ventricular assist configuration, a right-ventricular assistconfiguration, or a biventricular assist configuration. For instance, ifthe left-ventricular configuration is adopted, the rotary pump isconnected to receive flow from the left ventricle of the heart andreturn it to the aorta. Generally the rotary pump includes a stator(housing) having an inlet and outlet port, an impeller positioned withinthe stator and having impeller blades to create the pumped blood flow, amotor for rotating the pump and a suspension system. The blood entersthe inlet of the stator and is pumped by the rotating impeller throughthe housing to the outlet, and back into the patient'scirculatory—system.

There are two primary configurations that are used for rotary blood pumpconfigurations: axial flow and centrifugal flow. In the axial flowconfiguration, the pump configuration is similar to a cylinder withinlet flow port at one end and exit flow port at the other end. Thecentrifugal flow configuration is similar to a circular disk with aninlet flow port at the center of one side of the disk, orientedperpendicular to the plane of the disk, and a tangential exit flow portat the periphery of the disk, in the plane of the disk.

Studies have shown several problems with poor rotary blood flow pathdesign in both axial flow and centrifugal flow blood pumps includingthose with magnetic suspension. One of these problems is stagnationresulting in thrombosis or clotting. If the flow undergoes a low or zerovelocity region, it may experience thrombosis or clotting, where bloodresides on the pump structure. Such low or zero velocity regions areusually found in secondary blood paths in the pump. As the thrombosisbuilds up, a section or large clot may break off and embolize in theblood stream. If the clot occludes a blood vessel that enters the brainor other sensitive area, very serious conditions may develop, such asprofound organ dysfunction, such as seizure or severe brain damage.Another problem is hemolysis, where blood is exposed to high shearstresses in the rotary pump, usually near the impeller blades which moveat relatively high speed, and which may cause direct or delayed damageto the circulating blood. As the impeller applies forces to the blood,regions of turbulence and/or jet formation, can occur in poorly designeddevices.

Many rotary blood pump designs have been created to overcome thesebearing problems with their use as ventricular assist devices. It isdesired to have a bearing system with an expected operating lifetime of10 to 20 years, if possible. Generally, these bearings fall into threecategories: mechanical, hydrodynamic or magnetic bearings.

Some rotary blood pumps have mechanical or hydrodynamic bearings orhydrodynamic suspensions. For example, see U.S. Pat. Nos. 6,609,883 and6,638,011. Other rotary blood pumps have a combination of hydrodynamicbearings and permanent magnet bearings. For example, see U.S. Pat. Nos.5,695,471; 6,234,772; 6,638,083 and 6,688,861.

One type of rotary blood pump has mechanical bearings which require alubricant flush or purge with an external lubricant reservoir forlubricating the bearings and carrying away heat. For example, see U.S.Pat. Nos. 4,944,722 and 4,846,152. There are many disadvantages to thistype of pump. The percutaneous supply and delivery of the lubricantpurge fluid degrades the patient's quality of life and provides a highpotential for infection. Seals for the external lubricant arenotoriously susceptible to wear and to fluid attack which may result inleakage and the patient having a subsequent seizure. Also, an additionalpump is needed for delivery of the lubricant to the bearing, and if itfails the lubricated bearing freezes. Finally, the mechanical bearingshave a finite wear life, usually of a few years, and need to be replaceddue to the bearing wear.

There are axial flow rotary pumps with ceramic bearings presently underclinical trials. It is not known how long these bearings might last butexpected lifetimes based upon other applications are in the range of 2to 5 years. Also, there have been reported cases of thromboembolism insome patients. This has occurred while the patients are beinganticoagulated.

Rotary pumps have been developed with magnetic suspension to overcomethe earlier need for an external purge of lubricant or ceramicmechanical bearings. Utilizing a magnetically suspended impellereliminates direct contact between the rotary and stationary surfaces,such as found in mechanical bearings. For example, see U.S. Pat. Nos.5,326,344 and 4,688,998. Expected operating lifetimes of magneticsuspension systems range from 10 to 20 years. This type of rotary pumpwith magnetic suspension generally includes an impeller positionedwithin a housing, with the impeller supported and stabilized within thehousing by a combination of permanent magnets positioned in the impellerand the stator, and with an electromagnet positioned within the stator.The impeller is rotated by a ferromagnetic motor consisting of a statorring mounted within the housing, and electromagnetic coils wound aroundtwo diametrically opposed projections. The ferromagnetic impeller andthe electromagnetic coils are symmetrically positioned with respect tothe rotary axis of the pump impeller.

In magnetically suspended rotary blood pumps the gap between the statorand the impeller serves the competing purposes of allowing the blood topass through, as well as assisting with the magnetic suspension androtation of the impeller. For the blood flow, the radial gap is desiredto be large for efficient blood pumping, but for efficient magneticsuspension, the radial gap is desired to be small. Because of thecompeting gap requirements, other prior art pumps often include aprimary fluid flow region and a secondary magnetic gap. The primaryfluid flow radial gap region is large enough to provide forhydrodynamically efficient flow without traumatic or turbulent fluidflow. The secondary magnetic radial gap allows for fluid therethroughwhich is small enough to provide for efficient magnetic levitation ofthe central hub, which can be either the stator or the impeller.Examples of pumps with a blood flow path including both a primary andsecondary blood path can be found in U.S. Pat. Nos. 6,071,093;6,015,272; 6,244,835 and 6,447,266.

Some prior art blood pumps include a permanent magnet thrust bearingwhich has a relatively large diameter thrust disk with permanent magnetshaving an alternating polarity configuration on both the stator androtor components of the pump, but oriented in a radial configuration. Itis believed that the large thrust disk obstructs the blood path andcreates a tortuous blood path which is far from straight through thepump. The prior art pumps, however, include radially polarized permanentmagnet configurations.

Various sensing techniques have been used to locate and control therotor position of an active electromagnetic bearing. These techniquesinclude eddy current or inductive, capacitive, and laser sensors,commonly used in industrial applications of electromagnetic bearings.Laser sensors cannot be used because they cannot “look through” theopaque blood. Eddy current and inductive sensors require a magneticsource in the stator and a magnetic target in the rotor as well as amagnetic path running between the stator and rotor used to sense therotor position. Capacitance probes require an electrical path betweenthe stator and rotor which is generally not feasible with blood pumps.

There are several problems associated with the use of an eddy current orinductive sensor types in the gap in between the stator and rotor of animplantable miniature blood pump. For example, these types of sensorsrely on a clear magnetically un-obstructed pathway between the sensor“face” and the rotor surface. This means that the sensor body must beplaced within the stator housing with its “face” perpendicular to therotor surface. It is desired to avoid having any part of the body of thesensor placed within the fluid stream (blood) of the pump, yet placed itclose to the rotor magnetic target. One problem with these types ofsensors is the possible contamination of the blood stream if the softiron or other non-biocompatible sensor faces are exposed to the blood.Generally this is solved with the use of some sort of thin biocompatiblematerial covering the sensor face and target to avoid blood contact.Other problems are space constraints required for the sensor, and theenergy budget required for such sensors.

In addition, such rotary blood pumps include a motor to rotate theimpeller which, in turn, produces the needed blood flow. It is desirablethat the motor have very long operating life, and operate fault freeduring a range of time up to one or more decades of service. Some pumpsuse brushless DC motors for this purpose which have a compact andefficient design without brushes. There is no brush wear so the expectedlife of such pumps is very long. One issue with such pumps is assuringthat the motor will start in the necessary direction for the impeller topump. The proper start up direction of rotation can be an importantissue.

As noted above, magnetic suspensions often include at least one activecontrol electromagnetic bearing axis. In a radial bearing configuration,the electromagnet can consist of a set of soft iron magnetic poles in aconfiguration in the stator arrayed circumferentially around the rotorwith a clearance gap and imposing centering forces acting upon a softiron placed in the rotor. The current in the coils must be controlledproperly to achieve the desired centering purpose, allowing the rotor toproperly operate in the clearance space. The current in the coils areadjusted by an automatic control system. In order to carry out theautomatic force centering control method, there must be a sensor tosense the position or displacement of the rotor magnetic target, anelectronic means of active control to adjust the control currents in thestator coils, such as electronic controller boards and power amplifiersto provide the power.

The control methods for determining the coil currents in the magneticbearing of an active bearing can involve a manner of specifying how thecoil currents are to be obtained. Active magnetic bearings can becomposed of soft iron magnetic materials which have a significantlimitation in that they are subject to magnetic saturation at a certainlevel, typically at about 1 Tesla. The active control method should takethat fact into account. Also, the force exerted by an active magneticbearing is a nonlinear function of both the magnetic gap and the currentin the coils.

The most common method of dealing with both the magnetic materialsaturation and the nonlinearity is that of bias linearization, where asteady state bias current is imposed on each of the coil currents, whichproduces a magnetic flux in the soft magnetic iron poles ofapproximately one half of the magnetic saturation flux. Then aperturbation current is applied to produce changes in the coil currentsassociated with the poles on one side of the rotor relative to the otherside. In turn, when these differences due to higher coil currentsassociated with the poles on one side produce higher magnetic forces onthe rotor magnetic target compared to the other side, where lower coilcurrents associated with poles on the other side of the rotor producelower magnetic forces acting on the rotor magnetic target. The rotor hasa net force which is employed to center it in the clearance gap. The useof the bias linearization method, as just described, has a majordisadvantage that it has relatively high power consumption in the coils,and generates large heating in the coils which may overheat the activemagnetic bearing component of the rotary blood pump. Further, there arelimitations on this type of bias linearization which prevent the fullutilization of the magnetic force capacity of the active magneticbearing.

Another issue with regard to proper centered operation of the rotarypump impeller is the unbalance in the rotor. Rotating devices aresubject to mechanical unbalance as it is difficult to manufacture aperfectly balanced rotor. In addition, during operation within thepatient over a long period of time, additional changes in unbalance maytake place due to rotor component shifting, rotor rubbing, blood orblood products adhesion to the impeller surfaces, and other factors.

As the patient undergoes different levels of activity, the non-centeringforces acting upon the rotor change. When the patient is active, such asin walking or climbing stairs, the magnetic current biasing levels inthe active magnetic bearing are required to be high to provide highmagnetic centering forces. However, when the patient is sitting quietlyor sleeping, much less magnetic bearing centering force is needed.Higher bias current levels result in higher power consumption and higherheating.

In addition, centrifugal flow rotary blood pumps with magneticsuspension have been proposed. For example, see U.S. Pat. Nos.6,074,180; 6,595,762, and 6,394,769. It has been found, however, thatcentrifugal flow pumps are not easily implantable in either animals orhumans because the inflow and outflow cannulas are located at 90 degreesrelative to each other and in separate planes. In addition, suchcentrifugal pumps require convoluted secondary blood flow paths as partof the design.

SUMMARY OF THE INVENTION

It has been recognized that it would be advantageous to develop areliable ventricular assist device for permanent implantation in humans.In addition, it has been recognized that it would be advantageous todevelop a blood pump to reduce coagulation, avoid secondary flow paths,and provide an open, one-pass blood path. In addition, it has beenrecognized that it would be advantageous to develop a blood pump with areduced size, long operational life and lower power consumptionrequirements. In addition, it has been recognized that it would beadvantageous to develop a blood pump with a hybrid permanent magnet andelectromagnetic set with permanent magnets to manage greater forces(axial or thrust) and an electromagnet to manage lesser forces (radial).In addition, it has been recognized that it would be advantageous todevelop a blood pump with optimum configuration permanent andelectromagnetic bearings to enable the best blood pump flow performance.In addition, it has been recognized that it would be advantageous todevelop a blood pump with proper start up direction of rotation. Inaddition, it has been recognized that it would be advantageous todevelop a blood pump with control methods that consume less power andproduce less heat to facilitate an active magnetic bearing component.

The invention provides a blood pump with an impeller rotatably disposedand magnetically suspended within a cavity of a stator by a plurality ofmagnetic bearings (passive permanent and active electromagnetic) havingimpeller magnets on the impeller and stator magnets or coils/poles onthe stator. A motor includes impeller magnets on the impeller andcoils/poles associated with the stator. A single, annular blood flowpath extends axially through the cavity between the impeller and thestator, and between the impeller magnets on the impeller and the statormagnets or the coils/poles on the stator.

Additional features and advantages of the invention will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional perspective view of a bloodpump in accordance with an embodiment of the present invention;

FIG. 2 is perspective view of the blood pump of FIG. 1;

FIG. 3 is a longitudinal cross-sectional perspective view of a stator ofthe blood pump of FIG. 1;

FIG. 4 is a partially broken-away perspective view of an impeller of theblood bump of FIG. 1;

FIG. 5 is a side view of the impeller of FIG. 4, shown with infuser anddiffuser blades of the stator and showing inducer, impeller blade anddiffuser regions;

FIG. 6 is a cross-sectional schematic view of the blood pump of FIG. 1showing a magnetic suspension and rotating system;

FIG. 7 is a partial, side schematic view of the blood pump of FIG. 1;

FIG. 8 is a schematic end view of the blood pump of FIG. 1 showing anactive, electromagnetic bearing;

FIG. 9 is a partial end view of a prior art active bearing;

FIG. 10 a is a partial end view of the blood pump of FIG. 1 showing acombination of inducer blades and active, electromagnetic bearing poles;

FIG. 10 b is a partial perspective view of the blood pump of FIG. 1showing the combination of inducer blades and active, electromagneticbearing poles;

FIGS. 10 c-e are partial perspective views of the blood pump of FIG. 1showing one method for assembling the active, electromagnetic bearingpoles with the inducer blades;

FIGS. 10 f-h are partial perspective and end views of the blood pump ofFIG. 1 showing another method for assembling the active, electromagneticbearing poles with the inducer blades;

FIGS. 11 a and b are schematic end and side views of a sensor array ofthe blood pump of FIG. 1;

FIG. 11 c is a schematic side view of another sensor array of the bloodpump of FIG. 1;

FIG. 12 is a side schematic view of the blood pump of FIG. 1 showing theinducer, impeller blade and diffuser regions;

FIGS. 13 a and b are an end views of the inducer blades of the bloodpump of FIG. 1; and

FIGS. 14 a and b are side and end views of the diffuser blades of theblood pump of FIG. 1.

Reference will now be made to the exemplary embodiments illustrated inthe drawings, and specific language will be used herein to describe thesame. It will nevertheless be understood that no limitation of the scopeof the invention is thereby intended.

DETAILED DESCRIPTION OF PREFERRED AND ALTERNATIVE EXAMPLE EMBODIMENTS

As illustrated in FIGS. 1-8 and 10 a-14 b, an exemplary embodiment of acompact, axial flow, rotary blood pump, indicated generally at 10, isshown with a magnetic suspension and rotating system. Such a pump can beutilized as a ventricular assist device (VAD) for those who suffer fromcongestive heart failure (CHF). The pump 10 advantageously includes amagnetic suspension and rotating system that reduces size, has longoperational life and lowers power consumption requirements. In addition,the pump 10 advantageously includes an unobstructed one-pass blooddesign without a secondary blood path for any magnetic suspensionclearances, as opposed to previous magnetic suspension systems requiringboth primary and secondary blood paths. Thus, the pump 10 advantageouslyminimizes the incidence of flow stasis leading to thrombosis, as well ashemolysis by avoiding secondary flow paths

The magnetic suspension uses 1) one permanent magnet, passive, axiallycentering, thrust bearing; 2) one permanent magnet passive, radiallycentering bearing and 3) one active, electromagnetic, radial bearing, asdescribed in greater detail below. Thus, the power consumption isminimized because only one active electromagnetic bearing is employedthat consumes power, and the other bearings are permanent bearings thatconsume no power. In addition, the permanent bearings do not heat thepump, nor do they require wires, or any power supply or electroniccontrollers. Furthermore, this magnetic suspension configurationcontributes to the single pass blood path, without requiring anysecondary blood path, which also minimizes the power consumption, wirecount, power supplies, and electronic controllers.

The pump 10 includes a pump rotor or impeller 14 magnetically suspendedin an axial flow pump stator or housing 18. The stator 18 includes acavity 22 extending axially therethrough between an inlet 26 and anoutlet 28. The cavity 22 of the stator 18 can have a continuous andsealed liner 29 or can, separating stator components from the impellerand fluid passage, as described in greater detail below. The impeller 14is rotatably disposed in, and magnetically suspended in, the cavity 22or liner 29. The impeller 14 defines an axis of rotation 30 about whichthe impeller rotates. In addition, a gap or a fluid passage 32 isdefined between the impeller 14 and the stator 18 through which theblood flows. Thus, the blood enters through the inlet 26, flows aroundthe impeller 14, through the fluid passage 32, and out of the outlet 28,forming the single pass blood path. The cavity 22 and the stator 18 canalso extend along the axis of rotation 30. In addition, the inlet 26 andoutlet 28 can be aligned longitudinally or axially. The cavity 22 andimpeller 14 can have elongated, substantially cylindrical shapes thattaper at the ends.

The cavity 22 or pump 10 includes an inducer region 32 a, an impellerblade region 32 b, and a diffuser region 32 c, as shown in FIGS. 5 and12. The inducer region 32 a reduces a tangential flow component orstraightens the flow into the pump. The impeller blade region 32 bimparts rotational kinetic energy to the fluid. The diffuser region 32 cconverts the kinetic energy to static pressure.

The inducer region 32 a is located near the inlet 26, and includes aninfuser with one or more inductor blades 34. The inductor blades 34 aredisposed on the stator 18 at the inlet 26 of the cavity 22 and extend ina radial inward direction. In addition, the inductor blades 34 arealigned substantially axially with respect to the axis of rotation 30.Thus, the inductor blades 34 are configured to impose an axial flow (asopposed to a radial or circumferential flow) on the blood as it entersthe pump, and resist the impeller from inducing a circular flow upstreamof the pump. In one aspect, the inductor can include six bladescircumscribing the axis of rotation, as shown in FIGS. 3, 5, 10 a, 13 aand b. The inductor blades extend into the cavity, but without spanningthe cavity. The liner 29 can be formed over and around the inducerblades 34. It is of course understood that more or fewer inducer blades34 can be provided. In addition, it will be appreciated that the inducerblades can be curved or helical.

The diffuser region 32 c is located near the outlet 28, and includes adiffuser with one or more diffuser blades 36. The diffuser blades 36 aredisposed on the stator at near the outlet 28 of the cavity 22 and extendinwardly without spanning the cavity. The diffuser blades 36 are shapedand/or oriented substantially helically with respect to the axis ofrotation 30. Thus, the diffuser blades 36 are configured to straightenthe flow as it exits the pump. The diffuser can include three diffuserblades 36, as shown in FIGS. 3 and 5, or six diffuser blades 36 b, asshown in FIGS. 14 a and b. It is of course understood that more or fewerdiffuser blades can be provided. The diffuser blades can extend from theliner 29.

The diffuser region converts fluid velocities or kinetic energy intopressure due to the specific shape of the diffuser blades and thediffuser channel. In one aspect, the downstream diameter of the diffuserchannel can be slightly larger than the upstream diameter at an inlet tothe diffuser channel. The diffuser channel can have a divergence anglebeing usually less than 5 degrees in order to avoid flow separation. Theexpansion region in the channel will have a smooth increase incross-sectional area, thus reducing the axial velocity of the blood flowleaving the pump.

Stationary blades mounted to the diffusion shroud provide aconfiguration that aids in removing the tangential component of theabsolute velocity of the flow. The reduction in velocity further helpsto increase the pump's pressure rise and hydraulic efficiency. Thecurvature of the stationary blades is selected such that the flow entersthe diffuser blades with minimum hydraulic loss and leaves the pumpaxially. The assessment of the diffuser performance is given by therecovery factor, which is a function of the inlet and outlet diffuserflow velocities and the pressure loss within the diffuser due toresistance. The ideal case of a full recovery of the kinetic energy ofthe flow entering the diffuser is represented by a recovery factor ofunity. Maximum values for the recovery factor of 0.7-0.8 indicate anoptimum combination between the diameter ratio and length of thechannel. The recovery value decreases rapidly for large divergenceangles (>10 degrees) due to boundary layer separation.

The current diffuser blade geometry is designed to minimize hydrauliclosses at the design point. Therefore, for this operating condition, theleading edge of the diffuser blades perfectly matches the direction ofthe approaching blood flow velocity vector. At off design operatingconditions, there will be a mismatch between fluid approach velocityvectors and the leading edge angle of stationary blades causingadditional losses. However, for the operating range of the presentinvention, these hydraulic losses were maintained at an acceptablelevel, preserving the diffuser recovery factor.

The impeller blade region 32 b is disposed between the inducer anddiffuser regions 32 a and c. The impeller 14 can have an elongated bodywith one or more impeller blades or vanes 38 extending radiallytherefrom. For example, the impeller can have four impeller blades, asshown. It is of course understood that the impeller can be proved withmore or fewer impeller blades. The impeller blades 38 can have a helicalshape and/or orientation to drive the fluid or blood through the pump asthe impeller rotates. The impeller blades 38 and the diffuser blades 36can have opposite orientations so that the impeller blades 38 impartcircular flow in one direction and the diffuser blades 36 straighten theflow.

The magnetic suspension system includes a plurality of magnetic bearingsor bearing sets. Each bearing includes one or more impeller magnetsassociated with the impeller, and one or more corresponding statormagnets associated with the stator. The impeller and stator magnets aredisposed across the fluid passage 32 from one another, and substantiallyradially aligned with respect to the axis of rotation 30. The impellerand stator magnets can be annular or ring magnets with the stator magnetsurrounding or circumscribing and concentric with the impeller magnet.The fluid passage 32 can be substantially annular, and can extendbetween the annular magnets. In addition, the magnetic bearings caninclude a plurality or series of axially arrayed, abutting magnets oneach of the impeller and stator, as described below.

It has been recognized that, under normal operation, the largest forcethat to be controlled is the axial force due to the relatively largepressure change over the length of the pump. For example, the pressurechange across the pump can be as great as 150 mm Hg. The magneticsuspension system includes an axial or thrust bearing 40 to support theimpeller axially in the cavity 22. The axial bearing 40 includes aplurality of permanent magnets in an axially aligned, reverse polarityconfiguration to axially center the pump impeller. The axial bearing 40can be characterized as an array of adjacent bearing sets arrayedaxially with respect to the axis of rotation 30, with an array ofimpeller magnets 42 and an array of stator magnets 44. For example,three axial bearing sets can be disposed adjacent to, or abutting to,one another. Each bearing set includes an impeller magnet on theimpeller and a stator magnet on the stator. The impeller and statormagnets are radially aligned across the fluid passage 32 from oneanother. Thus, a plurality of adjacent impeller magnets 42 a-c isdisposed axially on the impeller, and a plurality of adjacent statormagnets 44 a-c is disposed axially on the stator. Adjacent impellermagnets, and adjacent stator magnets, have axially aligned polarities,and reverse polarities with respect to adjacent magnets. Thus, theaxially aligned polarity of one impeller magnet is reversed with respectto an adjacent impeller magnet. Similarly, the axially aligned polarityof one stator magnet is reversed with respect to an adjacent statormagnet. In addition, the impeller and stator magnets of each bearing sethave reversed polarity with respect to one another so that magnets ofthe axial bearing on opposite sides of the fluid passage have oppositepolarity. Thus, the axially polarity of one impeller magnet is reversedwith respect to a corresponding stator magnet across the fluid passage.

The axial bearing 40 can be constructed by several axially polarizedindividual components or rings. One ring is placed upon the impeller andone on the stator forming a fluid (blood) gap. FIGS. 3, 4, 6 and 7 showthe geometry of the magnetic ring pairs that form a thrust bearing. Thepolarization is different, as shown in FIG. 7, where the polarities arereversed. The North pole on one side of the fluid gap is placed acrossfrom the South pole on the other side of the fluid gap. The polaritiesare reversed at the other end of the rings. This configuration producesa positive axial stiffness and a negative radial stiffness.

A single pair of permanent magnets rings may not produce enough axialstiffness. The axial stiffness is strongly enhanced by constructing athrust bearing composed of several rings of reversed polarity, as shownin FIG. 7 for three rings. This combination of rings strongly increasesthe axial stiffness of the axial bearing. A different number of ringscan be used. The rings may or may not be of the same axial length.

The stator mounted permanent magnet configuration and the impellermounted permanent magnet configuration have a straight through clearancegap so that they can accommodate the once through axial blood pathwithout any axial obstruction. The axial permanent magnet uses no powerto axial center the rotor, so it assists with the reduction of powerconsumption. The configuration in this pump that produces this straightthrough flow path is the axially polarized permanent magnet alternatingpole configuration with magnets aligned axially on both the stator androtor without a large thrust disk.

The magnetic suspension system also includes a radial permanent magnetbearing 50 to support the impeller radially in the cavity 22. The axialbearing 40 can be characterized as at least a pair of adjacent bearingsets positioned axially with respect to the axis of rotation 30. Forexample, two axial bearing sets can be disposed adjacent to, or abuttingto, one another. Each bearing set includes an impeller magnet on theimpeller and a stator magnet on the stator. The impeller and statormagnets are radially aligned across the fluid passage 32 from oneanother. Thus, a plurality of adjacent impeller magnets 52 a and b isdisposed axially on the impeller, and a plurality of adjacent statormagnets 54 a and b is disposed axially on the stator. Adjacent impellermagnets, and adjacent stator magnets, have axially aligned polarities,and reverse polarities with respect to adjacent magnets, similar to thatdescribed above with respect to the axial bearing. In addition, theimpeller and stator magnets of each bearing set have the same polaritywith respect to one another so that magnets of the radial bearing onopposite sides of the fluid passage have the same polarity, oppositethat described above with respect to the axial bearing.

The radial bearing 50 can be constructed of axially polarized permanentmagnet rings. The rings can be of the same length. Alternatively, therings can have different lengths. One set of ring is placed upon theimpeller, and one set of rings on the stator forming a fluid (blood)gap. (The axial polarities are the same as indicated by the arrows withthe North pole at the head of the arrow and the South pole at the tailof the arrow.) The rotor and stator North poles are placed on oppositesides of the fluid gap while the rotor and stator South poles are placedon opposite sides of the fluid gap. This creates a positive stiffness sothat the rotor and stator have equal and opposite forces acting to keepthem from moving closer together. However, this configuration alsoproduces a negative axial stiffness, of twice the positive radialstiffness, that must be compensated for by other bearing components.

A single pair of magnetic rings may not provide enough stiffness to keepthe impeller centered. A higher stiffness radial bearing can beconstructed by combining several rings with similar polarity next to oneanother. This configuration strongly enhances the stiffness valuesbeyond the number which is obtained by multiplying the stiffness of onering by the number of rings. A different number of rings can be used.The rings may or may not be of the same axial length.

Thus, the axial and radial bearings 40 and 50 utilize a new permanentmagnetic pole configuration with compact, high magnetic strength magnetrings with axially polarized alternating polarity. This configurationenables axial suspension of the impeller and radial suspension of theimpeller at one end without any external power. Also, the permanentmagnet bearings do not require any feedback control or position sensorsto operate. These bearing configurations can be placed in the impellerand stator in a manner which does not intrude into the blood flow pathenabling a straight through blood flow path for the rotary blood pump.

The magnetic suspension system also includes a radial electromagneticbearing 60 to support the impeller radially in the cavity 22. The radialelectromagnetic bearing 60 can be a six pole, actively controlled,electromagnet with impeller magnets 62 disposed in the impeller 14, andcoils/poles (coils 64 and poles 66) associated with the stator 18. Theimpeller magnets 62 and coils/poles are positioned radially across thefluid passage 32 from one another. The stator can include a series ofradial stator poles 66 constructed of a non-permanent magnetic material,such as silicon iron, which are activated and powered by the coils 64wrapped around the legs as shown in FIG. 8 and similar materials forminga cylindrical configuration on the impeller. In one aspect, the wiringis configured in such a way that the currents generate magnetic fluxproducing a North pole in one of the electromagnet poles of a pair, andthe other produces a South pole in the other one of the pair. In theconfiguration shown, the six pole electromagnet shown in FIG. 8, thereare three pairs of poles. A smaller number or greater number ofelectromagnetic poles may be employed to reduce or increase the size ofthe bearing as needed with an associated reduction or increase in theforce capability of the bearing.

In one aspect, the active electromagnetic bearing 60 can include:position sensors, magnetic actuators, and a source that supplies anddrives the currents through each of the magnetic actuators. Referring toFIG. 9, an example of a typical, prior art radial active magneticbearing construction is shown with a radial stator 70 with coils 72 thatfrom the actuators, and a rotor 74 whose radial position is governed bythe amount of flux, or composite force, that is generated within each ofthe actuators. The stator generally is a single monolithic piece of“soft” magnetic material, such as silicon iron (SiFe), which provides alow reluctance pathway for the magnetic fields generated by theactuators. Generally, this radial stator assembly also provides a meansfor securing this structure to the housing, such as four through holes(one in each quadrant) that provide for axial attachment of the statorto the housing. The prior art assembly method for a radial active magnetbearing include “slipping” each of the radial coils 72 onto each “leg”of the stator 70, and then inserting and securing the stator into itsrespective housing. The purpose of the prior art active magnetic bearingis to provide the force, via the flux generated within the structure, toposition and hold the rotor 74 in its centered position.

In one aspect, the pump of the present invention can combine the infuseror inductor blades 34 with the active electromagnetic bearing 60. Thepoles 66 of the active bearing can extend into, or can be combined with,the inductor blades 34. Referring to FIGS. 10 a and b, the inducerregion of the stator 18 and a portion of the active electromagneticbearing 60 is shown with the active electromagnetic bearing 60 andinfuser blades 34 incorporated together. The electromagnetic bearingpoles 66 can be placed in the pump inducer where the poles are coveredby solid material in the shape of a fluid blade to strengthen andenhance the pump inlet flow. Thus, the bearing poles 66 can be disposedin the infuser blades 34. This dual use of the pole/blade configurationprovides a compact multi-use design for these pump components. This dualuse also makes efficient use of the space and volume allotted. Thus, theactive magnetic stator and inducer are combined, as are their twofunctions, into one composite dual use device.

The inducer can include a non-magnetic material, such as titanium, thatprovides a unimpeded magnetic pathway for the flux generated within thestator, while it also provides a means for sealing the fluid (blood)that passes through the interior of the inducer from being crosscontaminated by the stator magnetic components. This form of protectiveenclosure is referred to as a liner or “can” 29. It would be difficultto insert a rigid monolithic active magnetic bearing stator structurewithin the monolithic form of the inducer. Thus, a combined inducer andactive magnetic bearing stator is assembled, as shown in FIGS. 10 c-10e. Referring to FIG. 10 c, an active magnetic bearing leg and coilsubassembly 80 is shown with a stator backiron 82. An individual statorleg 84 with a “T”-shape or cross-section includes opposite “dovetail”surfaces on either end of the horizontal portion of the leg. Thesedovetail surfaces mate with an inverted or mating dovetail slot 85 inthe stator backiron 82. A coil 86 fits around the perimeter of thevertical portion of the “T”-shape and is shown coincident to the bottomof the horizontal portion of the “T”. Referring to FIG. 10 d, sixsubassemblies 80 are shown inserted into pockets 88 provided in theinducer or can 29. Referring to FIG. 10 e, the dovetails of thesubassemblies 80 are axial inserted within the dovetail slots 85 of thebackiron 82.

Referring to FIGS. 10 f-h another method of assembling a combined activemagnetic bearing and inducer is shown. An integral or monolithic leg andbackiron 90 includes a leg portion 92 and a 60 degree arc portion 94 ofthe completed backiron 96. A coil 86 fits around a perimeter of the legportion. A 60 degree arc has been used by way of example, because theinducer can include six blades. A different number of legs or blades maybe used, as well as unequal arc segments. Again, the leg portion 92 isinserted into pockets of the can 29.

As shown, the plurality of magnetic bearings can be positioned with theradial electromagnet bearing 60 disposed nearer the inlet 26 to thefluid passage; the radial permanent magnet bearing 50 disposed nearerthe outlet 28 to the fluid passage; and the axial permanent magnetbearing 40 disposed intermediate the radial electromagnet bearing andthe radial permanent magnet bearing.

In addition, the pump 10 includes a motor 150 with impeller magnets 154on the impeller 14 and coils/poles (coils 158 and poles 162) associatedwith the stator 18. For example, the motor can be a brushless DC motorwith no brushes to wear out and a compact, power efficient construction.In addition, the motor can have an offset stator pole structure suchthat it can only be started up in one direction—the proper or desireddirection for the impeller to pump.

Furthermore, the motor can be a unidirectional motor. The motor caninclude a brushless DC motor configuration which can only start-up inthe needed direction of movement consistent with the impeller flowdesign and a self-tuning controller. The motor can include off-setstator poles which taper to create a magnetic gap between a leading poleedge in a desired direction of rotation smaller than another magneticgap between a trailing pole edge in an opposite direction of rotation.The motor can be a six pole configuration with tapered poles, threephase stator winding and a four segment permanent magnet target in therotor. Thus, there are no brushes to wear out and the motor has acompact, power efficient construction. In addition, the motor has aspecial offset stator pole structure, such that it can only be startedup in one direction—the proper direction for the impeller to pump. Theproper startup torque direction is produced with a tapered pole design.The motor pole construction has a taper such that the magnetic gapclearance of the leading motor pole edge, in the direction of rotation,is made smaller than the magnetic gap clearance of the motor poletrailing edge, in the opposite direction of rotation. The motor can alsoinclude a self tuning controller with a microprocessor controllerinverter. Unlike previous rotary blood pumps that call for an angularposition sensor, the present motor and controller do not require anysensor to determine commutation or rotational speed. The self tuningcontroller utilizes auto-parameter tuning upon start up, in torqueoverload situations, high temperature protection, and active rotationalspeed control. This inverter provides high efficiency while reducing anyradio frequency noise generation.

The magnetic suspension system described above, along with the rotatingsystem or motor, provides a marked improvement over previous magneticsuspension systems requiring both primary and secondary blood paths. Thepresent magnetic suspension system enables an unobstructed, one-passblood design, without a secondary blood path for the magnetic suspensionclearances. Thus, secondary flow paths are avoided which minimize theincidence of flow stasis leading to thrombosis as well as hemolysis.

The single, unobstructed blood path, and the fluid passage, is definedby an annular gap positioned radially between all of the magneticbearings and the motor. Thus, all of the magnetic bearings have statormagnets disposed radially across the fluid passage from correspondingimpeller magnets. Similarly, the motor has coils/poles disposed radiallyacross the fluid passage from corresponding impeller magnets. Thus, theannular gap is positioned radially between the impeller and the stator,and positioned radially between all of the plurality of magneticbearings. The fluid passage or single, unobstructed blood path extendsthrough the stator and around the impeller, between the permanent magnetand electromagnetic bearings. Thus, the impeller is magneticallysuspended within the cavity of the stator without structure spanning thecavity of the stator.

The pump can be controlled and powered by a controller box, that may beimplanted or external to the body, and that can provide coil currents tothe motor and active bearing. The controller box can include controlelectronics or computers, and a power supply. The power supply caninclude a long term battery carried on the body, and a small internalbattery in the controller box for short term back up use. If the controlbox is implanted, the long term battery power can be supplied either bya transcutaneous wire or a high frequency transfer (telemetry) throughthe intact skin. If the control box is carried externally, long termbattery power can be supplied by wire.

Power amplifiers can be employed to operate the electromagnetic bearingcoils based upon input signals from coil control signal processingboards. The coil controller boards can be programmed with an automaticfeedback control algorithm to keep the pump impeller positioned at ornear the center of the fluid gap clearance when subject to variousfluid, gravitational or other disturbance forces. The automatic feedbackcontrol algorithm can utilize the rotor radial coordinate position, intwo coordinate directions, relative to the stator or pump housing andimpeller axial coordinate position relative to the pump housing as thefeedback signal. These impeller position signals can be provided bysensors, such as Hall sensors or eddy current sensors. The feedbacksignal may include other inputs, such as pump accelerations in one, two,or three directions as measured by an accelerometer.

The radial and axial positions can be detected by Hall sensors whichinclude very compact, low power electronic operated, sensitive sensorsof magnetic fields. Several of these sensors can be placed in the pumphousing in multiple radial positions, and at least two axial positions.At least some of the Hall effect sensors 200 can be placed where thefluid gap tapers so that the magnetic field varies with both radial andaxial position changes so that both are evaluated from a simplealgorithm and thus the position changes are measured in both directions.The Hall effect sensors can be powered by the same long term (or shortterm) battery system as the electromagnetic bearing.

Permanent magnets 204 can be placed in the impeller in positionsadjacent to the locations of the Hall effect sensors in the stator orpump housing. The permanent magnets 204 provide the changes in magneticfield signal, as the rotor moves radially or axially, for the Halleffect sensor to evaluate. These Hall effect sensors detect thedisplacement of the impeller relative to the sensor in both radial andaxial directions, and provide part or all of the feedback control signalused for the electromagnetic bearing, as well as the physiologicalcontroller. Also, they provide signals which will be monitored by thecontroller unit to provide alarms, or other suitable methods to make thepatient or medical personnel aware of existing or potential problems,such as impeller rubbing. Signals may be used for monitoring by the pumpcontrol unit, or telemetered to an external monitoring/alarm unit.

Using the Hall effect sensors eliminates the problems of spaceconstraints requirements for the sensors, the energy budget required forthe sensors, placing sensor faces within the stator housing,contamination of the blood stream, and thrombosis and clots. The Halleffect sensors use the Hall “effect” to measure the field surrounding amagnetic device. Linear versions of these devices are able to accuratelyplot the magnetic field intensity surrounding a magnetic device. FourHall effect sensors can be arranged in an orthogonal array, two on boththe X and Y axes, then by differentiating the axis pairs, the positionof the magnet within these devices can be obtained. One advantage ofusing a Hall effect sensor in this miniature blood pump is that the fluxlines emanating from the magnet will easily pass through the fluid(blood) without contamination, and the magnet and Hall effect sensor canboth be sealed behind in a non-magnetic barrier that is referred to as aliner or “can”.

Referring to FIGS. 11 a and b, one embodiment of a Hall effect sensorarray is shown. As show in FIG. 11 a, four Hall effect sensors (X+, X−,Y+, and Y−) are shown attached and mounted orthogonally to a printedcircuit board (PCB) as a Hall sensor array, and a cylindrical magnet 74is centered in between these Hall effect sensors. Referring to FIG. 11b, stylized magnetic flux lines are shown emanating from the magnet 70that represent only one plane (Y) of flux line distribution about themagnet, where these flux lines are shown intercepting the Y+ and Y− Halleffect sensor. It will be appreciated that if the magnet is centered inbetween the Y+ and Y− Hall effect sensor, these two devices will outputa voltage of equal amplitude. It will also be realized, that if theoutput from these two devices are assigned the +Y and −Y respectiverelationships, and these values are then differentiated, the signeddifferentiated output will be an indication of the magnet position aboveor below the abscissa, and the value of this output will be the amountof positional offset from the abscissa. Likewise, the X position of themagnet within the sensor array can be obtained by following this sameprocedure. The mathematical relationship for the X and Y positions wouldbe 3X=X−X+, and 3Y=Y−Y+. It will also be appreciated that the magneticflux lines from the magnet are impervious to any non-ferrous material,so that a biocompatible “can” or protective barrier that is made oftitanium, for example, would not impede or hinder the positionalinformation obtained from this device.

Referring to FIG. 11 c, another embodiment of a Hall effect arrayconfiguration is shown with two Hall effect arrays placed axiallysymmetric about the centerline and mid plane of a magnet. It will beappreciated that the X1, Y1, X2 and Y2 differentiated pairs will work asindependent sensors for determining the relative X and Y magnet positionat their respective locations. It will also be appreciated that inaddition to the X and Y positions, the relative axial location of themagnet can be derived by separately summing the all of X1 and Y1 Halleffect outputs without regards to the sign (31=(X1+)+(X1−)+(Y1+)+(Y1−)),while simultaneously doing the same with X2 and Y2 outputs (32).Assigning an arbitrary sign of + of axial motion towards the right (X2and Y2) arrays, and—as motion towards the left (X1 and Y1) arrays, andadding these two summations together will yield the direction of axialoffset as well as the Z value of the magnet position. The mathematicalrelationship for determining the Z position of the magnet, assumingmotion towards the right would be positive, would be Z=32−31.

The above described Hall effect sensors or arrays do not require anunobstructed vision of the impeller. Thus, the sensors can be separatedfrom the impeller and fluid passage by the lining or can. In addition,the sensors do not intrude into the fluid passage, and thus do notimpede the flow path or fluid characteristics. In addition, the sensorsdo not require any special surfaces to locate the position of a rotatingmember. For example, laser sensors require highly polished surfaces, andEddy Current (inductive) and capacitive sensors require a conductive(metallic) surface. In addition, the sensors do not require anadditional magnet to be added to the rotating member. For example, twopermanent magnet arrays can be placed within the impeller body, asshown. Therefore, the two Hall effect sensor arrays that are describedabove could be judicially placed within the stator to view the radialpermanent magnets on the impeller and the axial permanent magnets on theimpeller. Furthermore, the sensors can be used in conjunction with themotor characteristics (RPM and consumed power) to determine the pressuredifferential across the pump. This feature could be very important ininferring the high and low blood pressure in a patient.

Alternatively, the Hall effect sensors can be positioned to utilize theimpeller magnets of the axial and radial bearings, as opposed to theadditional magnets. Thus, two Hall effect sensor arrays can bepositioned on the stator, with one being positioned to sense a magneticfield produced by the impeller magnets of the axial permanent magnetbearing, and another positioned at a different axial location to sense adifferent magnetic field produced by the impeller magnets of the radialpermanent magnet bearing.

One or more accelerometers can be used to measure accelerations of thestator or pump housing in different directions. Also, velocitymeasurement devices may be employed to determine the velocity of thepump housing in different directions. The signals from these devices maybe employed to serve as feedback signals for the electromagnet, as wellas the physiological controller and/or alarms such as to indicate afall.

In addition, the active electromagnetic bearing itself can be viewedboth as an actuator and a sensor. Thus, the active bearing can be usedin a self-sensing mode to extract the position information from thecoil. An estimator can be built to filter the current signal and obtainthe position from the filtered signal. Such a technique eliminatesadditional sensors and electronics. Therefore, the number of wire leadsis reduced, so does the reliability.

Referring again to FIG. 4, the impeller can include a tie bolt 300 andexpendable material 304 that can be used to balance the rotor.

The impeller and diffuser can be manufactured by a titanium castingusing a lost wax method in which a precise wax model or positive isformed in a ceramic shell and negative. Liquid titanium can be pouredinto the ceramic shell, and the shell cracked open after cooling.Hydrogen pressure implantation can be applied to the cast object toremove any surface imperfections, followed by a chemical etch to preparethe surfaces for machining and polishing. The blood flow path can bepolished to a 10 micro-inch surface finish or better. The inlet cannulaand the inducer can be produced with standard metal forming techniques.The inlet cannula can be titanium tubing that is formed (bent andflared) into the desired shape. The inner surface can be polished to 10micro-inch surface finish. The inducer can be manufactured using acombination of CNC milling, wire electrical discharge machining (EDM)and plunge EDM techniques. Alternatively, the inducer could be cast asdiscussed above. Polishing can be accomplished using the extrude honemethod, which involves using a fine cutting medium, such as diamondchips, suspended within a slurry-like medium to polish and remove anysurface imperfections. The slurry can be pumped or passed along thesurfaces to be polished until desired surface finish is achieved.

In accordance with one aspect of the invention, the pump can beconfigured to pump fluids or liquids other than blood.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

1. A blood pump, comprising: a stator having a cavity extendingtherethrough; an impeller, rotatably disposed and magnetically suspendedwithin the cavity of the stator, the impeller defining an axis ofrotation, and the stator and impeller defining a fluid passagetherebetween; a plurality of magnetic bearings, including passivepermanent magnet and active electromagnetic bearings, suspending theimpeller within the cavity of the stator, and having impeller magnets onthe impeller and stator magnets or coils/poles on the stator; a motorincluding impeller magnets on the impeller and coils/poles associatedwith the stator; and a single, annular blood flow path extending axiallythrough the cavity between the impeller and the stator, and between theimpeller magnets on the impeller and the stator magnets or thecoils/poles on the stator.
 2. A blood pump in accordance with claim 1,wherein all the impeller magnets and corresponding stator magnets orcoils/poles of the magnetic bearings and motor are disposed radiallyacross the single, annular blood flow path.
 3. A blood pump inaccordance with claim 1, wherein the cavity of the stator has asubstantially cylindrical shape tapering at the inlet and the outlet;and wherein the impeller has a substantially cylindrical shape taperingat opposite ends.
 4. A blood pump in accordance with claim 1, furthercomprising: an inducer region with at least one inducer blade extendingradially inward from the stator near the inlet without spanning thecavity; and a diffuser region with at least one diffuser blade extendinginward from the stator near the outlet without spanning the cavity.
 5. Ablood pump in accordance with claim 1, wherein the single, annular bloodflow path extends axially through the cavity without any secondary flowpaths or recalculating flow paths.
 6. A blood pump in accordance withclaim 1, wherein all of the magnetic bearings and the motor share acommon longitudinal axis.
 7. A blood pump in accordance with claim 1,wherein the impeller is magnetically suspended within the cavity of thestator without structure spanning the cavity of the stator.
 8. A bloodpump in accordance with claim 1, wherein all of the magnetic bearingsinclude impeller magnets disposed in the impeller, and stator magnetsdisposed on the stator and around the cavity of the stator, without anystator magnet disposed in the cavity of the stator.
 9. A blood pump inaccordance with claim 1, further comprising: a can, radially surroundingthe cavity of the stator, and separating the coils/poles of the statorfrom the fluid passage.
 10. A blood pump in accordance with claim 1,wherein the plurality of magnetic bearings further comprises: a) aradial, active, electromagnet bearing, disposed nearer an inlet to thefluid passage, to radially support the impeller in the cavity,including: i) an impeller magnet, disposed nearer a leading end on theimpeller; and ii) a plurality of poles and coils, disposed on the statorradially across the fluid passage from the impeller magnet; b) an axial,passive, permanent magnet bearing, disposed intermediate along the fluidpassage, to axially support the impeller in the cavity including: i) aplurality of impeller magnets, disposed intermediate along the impeller,the impeller magnets having axially oriented polarities withsequentially altering polarity; and ii) a plurality of stator magnets,disposed on the stator radially across the fluid passage from theimpeller magnets, the stator magnets having axially oriented polaritywith sequentially alternating polarity; and iii) the impeller and statormagnets being radially aligned across the fluid passage from one anotherwith the polarity of the impeller and stator magnets oppositely alignedwith opposite polarities radially aligned across the fluid passage; andc) a radial, passive, permanent magnet bearing, disposed nearer anoutlet of the fluid passage, to radially support the impeller in thecavity, including: i) a plurality of impeller magnets, disposed near atrailing end of the impeller, the impeller magnets having axiallyoriented polarities with sequentially alternating polarity; and ii) aplurality of stator magnets, disposed on the stator radially across thefluid passage from the impeller magnets, the stator magnets havingaxially oriented polarities with sequentially alternating polarity; andiii) the impeller and stator magnets being radially aligned across thefluid passage from one another with the polarities of the impeller andstator magnets commonly aligned with common polarities radially alignedacross the fluid passage.
 11. A blood pump in accordance with claim 10,wherein the impeller and stator magnets of the axial, passive, permanentmagnet bearing have reversed polarity with respect to one another.
 12. Ablood pump in accordance with claim 10, wherein the impeller and statormagnets of the radial, passive, permanent magnet bearing have the samepolarity with respect to one another.
 13. A blood pump in accordancewith claim 10, further comprising: at least two Hall effect sensors,associated with the stator, one of the Hall effect sensors beingpositioned to sense a magnetic field produced by the impeller magnets ofthe axial, passive, permanent magnet bearing, and another Hall effectsensor positioned at a different axial location to sense a differentmagnetic field produced by the impeller magnets of the radial, passive,permanent magnet bearing.
 14. A blood pump in accordance with claim 1,wherein the plurality of magnetic bearings further includes an axialbearing to support the impeller axially in the cavity, including: anarray of adjacent bearing sets arrayed axially with respect to the axisof rotation, each bearing set including an impeller magnet on theimpeller and a stator magnet on the stator, the impeller and statormagnets being radially aligned across the fluid passage from oneanother; and adjacent impeller magnets and adjacent stator magnetshaving axially aligned polarities and reverse polarities with respect toadjacent magnets.
 15. A blood pump in accordance with claim 14, whereinthe impeller and stator magnets of each bearing set have reversedpolarity with respect to one another.
 16. A blood pump in accordancewith claim 1, wherein the plurality of magnetic bearings furtherincludes a radial permanent magnet bearing, including: at least a pairof adjacent bearing sets positioned axially with respect to the axis ofrotation, each bearing set including an impeller magnet on the impellerand a stator magnet on the stator, the impeller and stator magnets beingradially aligned across the fluid passage from one another; adjacentimpeller magnets and adjacent stator magnets having axially alignedpolarities and reverse polarities with respect to one another.
 17. Ablood pump in accordance with claim 16, wherein the impeller and statormagnets of each bearing set of the radial permanent magnet bearing havethe same polarity with respect to one another.
 18. A blood pump inaccordance with claim 1, wherein the plurality of magnetic bearingsfurther includes a radial electromagnetic bearing, including: impellermagnets, disposed in the impeller; and coils/poles, associated with thestator; the impeller magnets and the coils/poles positioned radiallyacross the fluid passage from one another.
 19. A blood pump inaccordance with claim 18, further comprising: inductor blades, disposedon the stator at an inlet of the cavity; the poles of the radialelectromagnet bearing being disposed within the inductor blades.
 20. Ablood pump, comprising: a) a stator having a cavity extendingtherethrough; b) an impeller, rotatably disposed and magneticallysuspended within the cavity of the stator, the impeller defining an axisof rotation, and the stator and impeller defining a fluid passagetherebetween; c) a radial, active, electromagnet bearing, disposednearer an inlet to the fluid passage, to radially support the impellerin the cavity, including: i) an impeller magnet, disposed nearer aleading end on the impeller; and ii) a plurality of poles and coils,disposed on the stator radially across the fluid passage from theimpeller magnet; d) an axial, passive, permanent magnet bearing,disposed intermediate along the fluid passage, to axially support theimpeller in the cavity, including: i) a plurality of impeller magnets,disposed intermediate along the impeller, the impeller magnets havingaxially oriented polls with sequentially altering polarity; and ii) aplurality of stator magnets, disposed on the stator radially across thefluid passage from the impeller magnets, the stator magnets havingaxially oriented polls with sequentially alternating polarity; and iii)the impeller and stator magnets being radially aligned across the fluidpassage from one another with the polls of the impeller and statormagnets oppositely aligned with opposite polls radially aligned acrossthe fluid passage; e) a radial, passive, permanent magnet bearing,disposed nearer an outlet of the fluid passage, to radially support theimpeller in the cavity, including: i) a plurality of impeller magnets,disposed near a trailing end of the impeller, the impeller magnetshaving axially oriented polls with sequentially alternating polarity;and ii) a plurality of stator magnets, disposed on the stator radiallyacross the fluid passage from the impeller magnets, the stator magnetshaving axially oriented polls with sequentially alternating polarity;and iii) the impeller and stator magnets being radially aligned acrossthe fluid passage from one another with the polls of the impeller andstator magnets commonly aligned with common polls radially alignedacross the fluid passage; f) a motor including impeller magnets on theimpeller and coils/poles associated with the stator; and g) a single,annular blood flow path extending axially through the cavity between theimpeller and the stator, and between the impeller magnets on theimpeller and the stator magnets or the coils/poles on the stator.